The present invention relates to a vibration sensor useful as a knocking sensor for detecting the occurrence of an engine knocking.
A typical conventional vibration sensor, shown in FIGS. 1 and 2 in transverse and side sectional views, respectively, comprises a casing assembly, constituted by a casing mount 4 having a threaded stud 6 formed integrally therewith and a cap member 5 mounted on the casing mount 4 to define a chamber therebetween, a ceramic vibrator 1 mounted inside the casing chamber on a base plate 2 through a support block 3', and a cable 7 electrically connected to electrodes 8 for the transmission of an electrical signal indicative of the occurrence of vibrations to an external electrical circuit. The vibration sensor is installed at a location, or a portion of an automobile engine, where vibrations are to be detected, with the threaded stud 6 firmly engaged thereto.
Since the frequency of vibrations detected by the vibration sensor is determined depending on the amount of projection, i.e., the effective length, of the vibrator 1 from the point of support to its free end extremity, this effective length must be exactly reproduced in each of vibration sensors when the latter are successively mass-produced. However, in the construction shown in FIGS. 1 and 2, the arrangement wherein the vibrator 1 is merely sandwiched between a retainer 8 and both of the base plate 2 and the support block 3' tends to pose a problem in that the effective length of the vibrator 1 may change when one or both of set screws 9 are loosened and/one or both of portions 20 of the vibrator 1 which are held in contact with the support block 3' and the retainer block 8, respectively, are deformed under the influence of the vibrations. In view of this, it is difficult to fix the frequency of vibrations to be detected at a constant value during the manufacture and, also, the use of the vibration sensor.